This invention relates to power supply apparatus for a radar system and, more particularly, to such apparatus which provides operating power for a tunable radar receiver, an IF amplifier used with that receiver and a radar transmitter, while minimizing the number of separate conductors which normally are provided between a "control box" and an "antenna unit" included in the radar system.
A typical radar system includes a "control box" and an "antenna unit". The control box includes a power supply for generating and supplying operating voltages for various components included in the antenna unit. The control box also includes signal processing circuitry, a radar display (such as a CRT) and other apparatus normally utilized by an operator in operating the radar system (e.g. a keyboard, a computer, etc.). The antenna unit of a typical radar system includes a rotating antenna for transmitting and receiving radar signals, transmitter circuitry responsive to transmit-control signals generated at the control box for supplying the antenna with radar signals to be transmitted, and receiving circuitry coupled to the antenna for receiving radar signals, reflected to the antenna and for producing video signals which, in turn, are supplied to the control box for processing, calculation and display. As is conventional, a cable is used to couple the control box to the antenna unit, this cable normally being provided with several individual conductors which supply control signals to the transmitter circuitry and to the receiver circuitry and which also supply video signals from the receiver circuitry to the control box. In addition, since the antenna unit normally is remote from the control box, operating power is generated at the control box and supplied to the antenna unit. Such operating power typically includes operating voltages for the transmitter circuitry and for the receiver circuitry, as well as an operating voltage for the usual intermediate frequency (IF) circuitry normally provided in or used with the receiver circuitry. Still further, although the transmitting and receiving circuitry are designed to operate at the same frequency, it is not unusual if the particular frequency to which the receiving circuitry is tuned differs, to a small degree, from the frequency to which the transmitting circuitry is tuned. Accordingly, to compensate for this frequency difference, or drift, a tuning voltage often is supplied from the control box to the receiving circuitry to provide electronic tuning so as to bring the receiving circuitry into a proper frequency relationship, thereby compensating for frequency drift.
Radar systems of the aforementioned type find ready application in a marine environment. As is conventional, the ship (or other) host vessel on which the radar system is located provides an electrical power supply from which the aforementioned transmitter, IF and tuning power supplies normally are derived. Suitable power supply circuitry usually is found in the control box; and the resultant power supply voltages are supplied to the antenna unit, thereby providing suitable operating voltages to the transmitter, the receiver and the IF electronics. However, one disadvantage of the conventional arrangement resides in the fact that the length of the cable which connects the control box to the antenna unit may be of variable length. That is, this length might not be known precisely in advance and, thus, when the radar system is installed, various adjustments are needed in the power supply circuitry at the control box so as to accommodate the particular length of the cable then in use. As is known, the voltage drop along a cable and, thus, the power loss presented thereby, is a function of the length thereof. When installing cables of longer than expected length, the operating voltage levels produced at the output of the power supply circuitry in the control box might have to be increased. Conversely, for cables of shorter than expected lengths, such operating voltage levels might have to be reduced. However, it was important that the IF power supply voltage and the receiver tuning voltage were of particular, predetermined values. Thus, adjustments in the power supply circuitry at the control box were necessary to compensate for different cable lengths while maintaining such predetermined voltage values.
Another disadvantage of prior art power supplies used in conventional radar systems is the requirement of several individual conductors included in the coupling cable which normally interconnects the control box and the antenna unit. Typically, a separate conductor is needed to provide operating power for the transmitter and receiver electronics, another conductor is needed to provide a separate power supply voltage to the IF electronics and yet another conductor is needed to provide a tuning power supply voltage to the receiver electronics. It is desirable to reduce the number of such conductors in the coupling cable; and it would be particularly advantageous to eliminate, if possible, the use of a separate conductor to provide an IF power supply to the IF electronics included in the antenna unit. As examples, a typical tuning power supply voltage generated at the control box is on the order of about 35 volts DC, and a typical IF power supply voltage generated at the control box is on the order of about 12 volts DC.
Usually, in conventional antenna systems, the control box and the antenna unit are designed independently of each other and are not necessarily matched. Matching occurs when the system is installed on, for example, a ship, and this matching takes into account the particular length of the cable extending between the control box and the antenna unit as well as other factors, such as the range over which the receiving circuitry should be tuned. Thus, a "fine" adjustment normally is needed to match a uniquely designed control box with a uniquely designed antenna unit.